(a) The classical radius of an electron is defined as r c = e 2 /4 0...

(a) The classical radius of an electron is defined as r_c = e²/4πε₀m_e in natural units. What is its value in fm?
(b) A simple classical model of the electron is to regard it as a sphere of uniform charge density, whose radius R is such that the electrostatic potential accounts for the whole electron mass. Derive the value of R, expressing it in terms of the classical radius defined above.